linux-kernel - Re: [tip:timers/core] ntp: Fix integer overflow when setting time

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Message-ID: <4F62978A.7000009@zytor.com>
Date:	Thu, 15 Mar 2012 18:29:46 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	mingo@...hat.com, hpa@...or.com, levinsasha928@...il.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de
CC:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:timers/core] ntp: Fix integer overflow when setting time

On 03/15/2012 02:53 PM, tip-bot for Sasha Levin wrote:
> Commit-ID:  a078c6d0e6288fad6d83fb6d5edd91ddb7b6ab33
> Gitweb:     http://git.kernel.org/tip/a078c6d0e6288fad6d83fb6d5edd91ddb7b6ab33
> Author:     Sasha Levin <levinsasha928@...il.com>
> AuthorDate: Thu, 15 Mar 2012 12:36:14 -0400
> Committer:  Thomas Gleixner <tglx@...utronix.de>
> CommitDate: Thu, 15 Mar 2012 21:41:34 +0100
> 
> ntp: Fix integer overflow when setting time
> 
> 'long secs' is passed as divisor to div_s64, which accepts a 32bit
> divisor. On 64bit machines that value is trimmed back from 8 bytes
> back to 4, causing a divide by zero when the number is bigger than
> (1 << 32) - 1 and all 32 lower bits are 0.
> 
> Use div64_long() instead.
> 

Perhaps we should use the same kind of multiply-and-shift tricks we're
doing for jiffies conversion?  If nothing else it ought to perform better.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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